The on-again, off-again saga of NetShare, an iPhone tethering application, continued over the weekend as Apple briefly returned the program to the App Store on Friday, but then yanked it from the mart a second time.

The NetShare application, which lets iPhone owners share the phone's EDGE or 3G cellular Internet connection with a notebook computer, reappeared Friday for several hours on Apple's App Store after being pulled Thursday. By approximately 10 p.m. PDT Friday, however, NetShare again went missing.

As of 3 p.m. Sunday, NetShare remained unavailable.

Developer Nullriver had no idea why its software had been reposted to the App Store on Friday, or why it had been removed later in the day. "NetShare is now back up and available from the App Store!" the company said midday Friday in an update to a statement posted to its Web site. Hours later, it updated the online statement. "Apple has taken it down again, with no explanation yet again," Nullriver said early Saturday.

Some users, including blogger Seth Weintraub, were able to snatch a copy of NetShare during the hours it was available on Friday.

Neither Apple or Nullriver has responded to requests for comment made early Friday, after NetShare's first disappearance from the App Store.

AT&T, Apple's exclusive network partner in the United States, does not officially allow users to tether a notebook to their iPhones, although it offers the service for $15 extra per month to owners of a wide range of handsets sold by LG, Motorola, Nokia, Research In Motion, Samsung, and others.

The terms for the plans offered by AT&T for the iPhone, for example, include language that forbids users from tethering: "Furthermore, plans (unless specifically designated for tethering usage) cannot be used for any applications that tether the device (through use of, including without limitation, connection kits, other phone/PDA-to-computer accessories, Bluetooth or any other wireless technology) to Personal Computers (including without limitation, laptops), or other equipment for any purpose."

Some users, however, pointed out that iPhone tethering isn't explicitly banned by all mobile operators, and that NetShare may show up in the App Store for users outside the United States. "The app may not violate a [terms of service agreement] of a different iPhone carrier, but in the US it does violate AT&T's TOS," said someone identified as "janey" in a thread on a MacRumors' message forum. "Apple has separate App Stores for the countries. It looks like it's an Apple ****up selling it in the US App Store."

Nullriver held out that hold as well. Its online statement concluded: "At the very least, we hope Apple will allow it to be used in countries where the provider does permit tethering."

When it was available on the App Store, NetShare was priced at $9.99. By the agreements it strikes with developers, Apple keeps 30 percent of all App Store sale revenues.